I have just checked myself and this is a bug please log it with Customer Support. In the meantime if you add the properties to the Central Library property file as a user property it should work around this issue.

Adding them to the PRP file as a workaround will allow you to add them to the symbol in the symbol editor. It won't affect the auto update, it simply by-passes the checking mechanism inside the symbol editor that is preventing you saving them on the symbol.

Once you have added them to the symbol successfully you can delete them from the prp file.

Alternatively you could try adding the property via the Console Window, the syntax to do this is as follows:

setattrib -index 0 -owner ICDBDXD 'symbolname.1' @Name {}

This is using the older 2007.8 syntax of the API which bypasses the new checking mechanism also. You should then be able to set the visibility etc via the Properties Pane.

I have made engineering aware of the issue and they are looking at it. If you log this with Customer Support we will be able to track it through our system.